Skip this chore: Cleaning your air conditioner condenser probably won't make it work better

Skip this chore: Cleaning your air conditioner condenser probably won't make it work better
Scratch this off your to-do list. Credit: Florence Yuill, CC BY-ND

I asked my neighbor who hoses off his air conditioner condenser every spring why he does it. "Because my dad always told me I had to," he said.

Conventional wisdom like what my neighbor's dad imparted may always seem right. But through my HVAC scholarship – the study of heating, ventilation and air-conditioning systems – I've learned that this particular presumption is probably wrong.

Dirty equipment

The equipment I'm talking about washing is the outdoor part of central air-conditioning systems that move heat from homes into the outdoors.

Technically known as condenser coils, they are usually about the size of a large garbage can but they can be as small as a bucket or as big as a refrigerator. Some are protected by louvered grilles but most are exposed to the elements. Their metal fins help transfer heat to the air. They contain tubes that carry the hot refrigerant, which gives off heat as it condenses.

Stuff like windblown seeds, dust and grass clippings tends to collect on the coil surface. Most homeowners and HVAC companies envision that this untidy-looking stuff acts like an insulating blanket, slowing down the passage of heat from inside to outside. Any debris that accumulates would also interfere with airflow over the coil, further restricting the system's ability to expel heat.

Skip this chore: Cleaning your air conditioner condenser probably won't make it work better
Close-up of 7 grams of dirt per square foot on an air conditioner condenser and that same condenser after it’s cleaned. Credit: Mehdi Mehrabi, CC BY-SA

The nitty-gritty

Mehdi Mehrabi, an architectural engineering graduate student, and I set out to learn the extent to which dirty residential air conditioners are less efficient than clean ones. What we found astonished us – and many of the other experts in this field.

Previous work on this question simulated outdoor dirt with in a laboratory setting, or used reduced airflow as a proxy for the effects of dirty coils. Although it's necessary to carefully to control operating conditions, we took a novel approach: collecting condensers that had gotten dirty through ordinary residential use, and bringing them to the lab for study with a special test apparatus.

This meant that they were coated in real-world dust and other crud in everyday amounts. We tested the dirty air conditioners, then washed them thoroughly with a garden hose and tested again. We also used a commercial coil cleaning fluid and tested them for a third time.

Surprisingly, we found that dirty air conditioner condensers often perform better than clean ones. The change in condenser coil heat transfer performance ranged from a 7 percent increase to a 7 percent decrease for the coils we tested. The average change was … none at all.

Skip this chore: Cleaning your air conditioner condenser probably won't make it work better
Close-up of 17 grams of dirt per square foot on an air conditioner condenser and that same condenser after it’s cleaned. Credit: Mehdi Mehrabi, CC BY-SA

The coil that registered a 7 percent improvement after getting cleaned up looked quite dirty, with 7 grams of dirt per square foot of coil surface area. But the coil that performed 7 percent worse was even dirtier, with 17 grams of dirt per square foot. It was so filthy, in fact, that it was nearly impossible to see the metal fins before we gave it a wash. Most of the condenser coils we tested in the lab were cleaner than both of those.

No insulating blanket

To see how the equipment's performance could improve by getting dirty, we did further testing.

That next round of study suggested that the accumulated dirt stirs up the air passing over the condenser coils. Technically called "turbulence," these little gusts can transfer away from the coil better. For some coil designs, this can cause the equipment to perform better when it's dirty than when it's clean. This is true even when the dirt has reduced the airflow rate.

If your home has one of these things, you are probably wondering whether you should you wash your own condenser. Here's what you should know.

Skip this chore: Cleaning your air conditioner condenser probably won't make it work better
The author, doing a chore that his own research has found to be pointless. Credit: Florence Yuill, CC BY-SA

Cleaning your air conditioner might make it run better. It might make it run worse. But it probably won't make any difference. I now personally believe in skipping this task, unless the is so dirty that it's hard to see the metal fins. Although, if it will make you feel better, go ahead and hose it down. To be honest, that's what I plan to do from now on.

Letting go of deep-seated beliefs of any kind is hard, whether it's that dieting makes you lose weight in the long run – something recent studies do not support – or if this particular home maintenance ritual is justified. As news of our findings spreads, I'm bracing for some unpleasant responses from people who might lose out if the condenser-cleaning business dries up and others who simply refuse to accept that there was no basis for the on this question.


Explore further

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Provided by The Conversation

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Citation: Skip this chore: Cleaning your air conditioner condenser probably won't make it work better (2019, March 22) retrieved 23 October 2019 from https://phys.org/news/2019-03-chore-air-conditioner-condenser-wont.html
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User comments

Mar 22, 2019
We're close to April Fool's Day and this article has prank written all over it. I'm a bit surprised though that Physorg would print something that discourages people from increasing their energy efficiency through routine maintenance.

Mar 22, 2019
"Cleaning your air conditioner might make it run better. It might make it run worse. But it probably won't make any difference... Although, if it will make you feel better, go ahead and hose it down. To be honest, that's what I plan to do from now on."

Published by "The Conversation," whose motto is: "Academic rigor, journalistic flair."

I'd say it's more click-baity tabloidy sensational flair than rigor, and it seems to defy reason itself and encourage its readers to just think less. Go ask an engineer if a heat exchanger works best when blocked and then marvel at how this article could ever have been written much less published.

Mar 22, 2019
Oh look, they cleaned 9 condensing units and fouling samples from two US locations and they want $15 for you to read the paper.

Mar 23, 2019
A bit of dirt isn't going to make a difference in the cooling performance, but it is going to make a difference in the rate of corrosion, because the dust and grime retains moisture and works as a sponge that keeps the metal surfaces from drying out.

It's like a car - if you don't wash it every now and then, it rusts faster. Aluminum corrodes too, especially since the radiators are welded together with zinc so it's not pure aluminum but an alloy.

Mar 23, 2019
Go ask an engineer if a heat exchanger works best when blocked and then marvel at how this article could ever have been written much less published.


A shiny metal surface isn't the best radiator. For the basic physics of it, surfaces that reflect don't radiate well, whereas surfaces which absorb radiation well - rough matte black - are also better at releasing and radiating it out.

Back when they started building central steam heating in buildings, they discovered that painting the radiators black made them give more heat. The paint is somewhat insulating, but the layer is so thin that it actually improves performance by making the surface give out heat more. We use this effect today in computers where the aluminum heatsinks are anodized matte rather than shiny - the oxide layer is insulating, but because it's rough and dull it's more efficient at radiating heat out.

Mar 23, 2019
Sorry, the aluminum isn't welded, it's brazed using zinc.

They form a galvanic pair where, once corrosion sets in, the heat exchanger comes apart at the seams.

Mar 23, 2019
I suspect, where the performance decreased, the dirt on the surface was forced deeper into the fins, during the washing.

the oxide layer is insulating, but because it's rough and dull it's more efficient at radiating heat out.

Could it be, that in making it rough, the surface area is increased and thus radiates better.

Mar 24, 2019
The first 3 trolls hand waved. While it is true that Conversation has non-rigorous and opinionated article the basis was published science, science do cost but above all publishing unfortunately still cost - don't blame the scientists.

I suspect, where the performance decreased, the dirt on the surface was forced deeper into the fins


Well, we don't know, and suspicion makes no science. But please be our guest and make the necessary experiments!

Mar 24, 2019
I'd like to know if they tested in ambient temperatures of 90F and 60% humidity.
That's Real world conditions.

Mar 25, 2019
The first 3 trolls hand waved. While it is true that Conversation has non-rigorous and opinionated article the basis was published science, science do cost but above all publishing unfortunately still cost - don't blame the scientists.

I suspect, where the performance decreased, the dirt on the surface was forced deeper into the fins

Well, we don't know, and suspicion makes no science. But please be our guest and make the necessary experiments!

Jackass goes...HAWW..HEE...HAWW...HEE..
Hey jackass, science begins with hypothesis.

Mar 25, 2019
Go ask an engineer if a heat exchanger works best when blocked and then marvel at how this article could ever have been written much less published.


A shiny metal surface isn't the best radiator. For the basic physics of it, surfaces that reflect don't radiate well, whereas surfaces which absorb radiation well - rough matte black - are also better at releasing and radiating it out.


This would be relevant if the discussion were about a blackbody radiator rather than a convective heat exchanger operating on forced air movement.

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